Differential Test Circuits for EMI-Resistant Low Current Measurement
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Solution Overview
Problem
Conventional apparatuses for measuring device currents are susceptible to electromagnetic interference (EMI), leading to reduced measurement accuracy for low device currents, especially in production environments, which affects test throughput and flexibility.
Innovation Solution
The apparatus employs two identical circuits to supply test voltages and sense output voltages, allowing for the elimination of EMI through proper signal processing, thereby enabling accurate measurement of low device currents without increasing integration time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional single-circuit test apparatus is used to measure device current, then the apparatus structure is simple, but measurement accuracy deteriorates due to EMI susceptibility
Solution Approach 1:
The patent employs two identical test circuits that are copies of each other, both connected to different terminals of the DUT. These identical circuits experience the same EMI conditions, allowing the measurement system to differentiate between EMI-induced signals and actual device current signals through differential processing, thereby achieving high measurement accuracy without increasing overall system complexity
Solution Approach 2:
The patent introduces a differential measurement approach where the difference between the two identical circuits' outputs is used to eliminate EMI. The EMI acts as a common-mode signal that is rejected through differential processing, while the actual device current signal is preserved, effectively using the difference signal as an intermediary to separate useful information from interference
2Measurement precision
If integration time is increased to suppress EMI, then measurement accuracy improves, but test throughput deteriorates
Solution Approach 1:
By using two identical parallel test circuits that simultaneously measure the device current under the same EMI conditions, the system eliminates the need for increased integration time. The differential processing of the two identical circuits' outputs allows for real-time EMI rejection while maintaining high test throughput
Solution Approach 2:
The patent converts the harmful EMI into a beneficial common-mode signal that can be rejected through differential processing. Instead of trying to filter out EMI after it has corrupted the measurement (which would require increased integration time), the system uses the identical EMI exposure of both circuits to create a differential signal that inherently rejects EMI while maintaining fast measurement speed
3Measurement precision
If shielding or short test lines are used to suppress EMI, then measurement accuracy improves, but device complexity and implementation effort increase
Solution Approach 1:
The patent uses two identical test circuits as a form of copying that inherently rejects EMI through differential processing. This approach avoids the need for physical shielding or shortened test lines, achieving EMI suppression through circuit design rather than physical modification, thereby reducing implementation effort while maintaining measurement accuracy
Solution Approach 2:
The patent changes the measurement approach from single-circuit direct measurement to two-circuit differential measurement. By changing the circuit configuration parameters and using identical parallel circuits, the system achieves EMI rejection without altering the physical layout or adding shielding, simplifying the overall implementation
Data Source
AI summary
An apparatus for measuring a device current of a device under test (DUT) includes a first circuit including a first terminal for coupling to a first connection terminal of the DUT. The first circuit is configured to supply a first test voltage for the first terminal and to output a first output voltage sensed at the first terminal. The apparatus further includes a second circuit having a second terminal for coupling to a second connection terminal of the DUT. The second circuit is configured to supply a second test voltage for the second terminal and to output a second output voltage sensed at the second terminal. The apparatus further includes a third circuit configured to determine the device current of the DUT based on the first output voltage, the second output voltage, the first test voltage and the second test voltage. The first circuit and the second circuit are identical.